The present description relates generally to methods and systems for calibration of a sensor system, and more particularly to calibration of differential sensing systems.
Various types of sensor systems have been used to measure the distance between two objects. One of such sensor systems includes a two-channel differential sensing system. In a two channel differential sensing system, various error sources that affect the two channels uniformly can be eliminated or reduced. Matching a response of the two channels is of utmost importance to be able to realize the benefits of the differential measurement. Any mismatch in the response of the two channels results in significant error in a measurement. For example, the error in clearance measurement results in inaccurate displacement between a shroud and a turbine blade of a turbine. It is therefore desired to dynamically and periodically check and correct the matching of the response of the two channels in the system. Variation in electronic components due to temperature effects and long term drifts are two reasons for change in response of the channel.
Various techniques in circuit design have been utilized to reduce the temperature coefficient of circuits and to reduce the effect of the drifts. However, these techniques don't ensure measurement accuracy over a long period of time. A commonly used technique is use of temperature compensated components in the sensor system. Another commonly used technique is use of very low drift components. Both of these methods reduce the variation, but make no provision for detecting and correcting drifts and variations over time and temperature. Current clearance sensing systems rely heavily on frequent lab calibration to address this problem. For example, for a flight system that requires many years of service without human intervention, calibration must be done in a transparent way and must not require the system be taken apart, or any human intervention.